@article{CTGDC_1993__34_4_305_0,
     author = {Gordon, Robert},
     title = {Crossed modules as $G$-categories},
     journal = {Cahiers de Topologie et G\'eom\'etrie Diff\'erentielle Cat\'egoriques},
     pages = {305--319},
     publisher = {Dunod \'editeur, publi\'e avec le concours du CNRS},
     volume = {34},
     number = {4},
     year = {1993},
     mrnumber = {1253173},
     zbl = {0801.18010},
     language = {en},
     url = {http://archive.numdam.org/item/CTGDC_1993__34_4_305_0/}
}